whichapp

#!/usr/bin/env bash
# Print the absolute path of the executable GNOME would use to open the given file.
# On failure, print a diagnostic to stderr and exit 1.
#
# Usage:
#
#   whichapp <FILE>
#
# Examples:
#
#   whichapp ~/Documents/notes.txt
#   whichapp image.png
#
# author: andreasl
set -euo pipefail

show_help() {
    script_name="${0##*/}"
    msg="${script_name}\n"
    msg+="Print the absolute path of the executable GNOME would use to open the given file.\n"
    msg+="On failure, print a diagnostic to stderr and exit 1.\n"
    msg+="\n"
    msg+="Usage:\n"
    msg+="  ${script_name} [OPTIONS] <FILE>\n"
    msg+="\n"
    msg+="Options:\n"
    msg+="  -h, --help    Print this help message and exit.\n"
    msg+="\n"
    msg+="Examples:\n"
    msg+="  ${script_name} ~/Documents/notes.txt\n"
    msg+="  ${script_name} image.png\n"
    printf "$msg"
}

case "${1:-}" in
-h | --help)
    show_help
    exit 0
    ;;
"")
    show_help >&2
    exit 1
    ;;
esac

file="$1"

mime=$(gio info --attributes=standard::content-type "$file" |
    awk '/content-type/ {print $NF; exit}')

desktop=$(gio mime "$mime" | awk -F': ' '
    /^Default application/ { def = $2 }
    /^Registered applications:/ { reg = 1; next }
    reg && /^\t/ && !first { gsub(/^\t/, ""); first = $0 }
    END { print (def ? def : first) }')

[[ -z $desktop ]] && {
    echo "whichapp: no handler for $mime" >&2
    exit 1
}

search_dirs=(
    "${XDG_DATA_HOME:-$HOME/.local/share}/applications"
    /usr/local/share/applications
    /usr/share/applications
    "$HOME/.local/share/flatpak/exports/share/applications"
    /var/lib/flatpak/exports/share/applications
    /var/lib/snapd/desktop/applications
)

path=
for dir in "${search_dirs[@]}"; do
    [[ -f $dir/$desktop ]] && {
        path=$dir/$desktop
        break
    }
done
[[ -z $path ]] && {
    echo "whichapp: $desktop not found" >&2
    exit 1
}

cmd=$(grep -m1 '^Exec=' "$path" | cut -d= -f2- |
    sed -E 's/%[UFufick]//g' | awk '{print $1}' | tr -d '"')

command -v "$cmd" || {
    echo "whichapp: cannot resolve $cmd" >&2
    exit 1
}